The present invention generally relates to a fixing apparatus and more particularly, to a fixing or fusing apparatus, for example, for use in an electrophotographic copying machine arranged to apply an offset phenomenon prevention liquid or solution such as silicone oil and the like onto the peripheral surfaces of fixing rollers through applicator means.
Generally, in the fixing or fusing apparatus, for example, of heat-pressure or roll type commonly employed for fixing or fusing developed toner powder images of an original formed by a copying machine in a known manner onto copy material such as copy paper sheets, and including upper and lower fixing rollers contacting each other for simultaneous rotation, with proper heating means provided therein, when silicone oil or the like as a solution for preventing the undesirable offset phenomenon is applied onto the surface of one of the fixing rollers by the applicator means, the amount of silicone oil adhering to the surface of the fixing roller tends to remain unevenly distributed over said surface, and if the unfixed toner powder images formed on the copy paper sheet are to be fused in the above state as the copy paper sheet is passed between the upper and lower fixing rollers, various problems related to excessive application of the silicone oil such as soiling of the copy paper sheets, wetting and swelling of silicone rubber layers or the like of the fixing rollers, etc. are likely to take place.
In order to overcome the disadvantages as described above, the present inventors have already proposed a fixing apparatus of silicone oil application system as shown in FIG. 1 which includes an upper fixing roller 4 of silicone oil impregnation type constituted by a cylindrical metallic core member 1 covered with a thin silicone rubber layer 2 applied onto its peripheral surface and having a heater member 3 incorporated therein for heating its surface, a lower fixing roller 7 also of the silicone oil impregnation type constituted by a cylindrical metallic core member 5 covered with a thick silicone rubber layer 6 applied onto its peripheral surface, with the lower fixing roller 7 being adapted to rotate in the direction indicated by the arrow "b" following rotation of the upper fixing roller 4 in the direction of the arrow "a" by suitable driving means (not shown), an offset prevention solution supplying and applicator member 10 immersed at its one end in the silicone oil 9 contained in a tank 8, intermittent application means (not shown) which causes the member 10 to contact, under a predetermined pressure, an applicator roller 11 kept in contact with the lower fixing roller 7 so as to follow the rotation of said roller 7, only during one rotation of the applicator roller 11 for each copying of one copy paper sheet and which brings said member 10 back to the original position spaced from the applicator roller 11 after the one rotation of said roller 11 for supplying the silicone oil 9 thus applied onto the applicator roller 11 further to the upper fixing roller 4 through the lower fixing roller 7 so as to make it possible to fix the unfixed toner images on the copy paper sheet P passed between said rollers 4 and 7, and a blade 12 arranged to contact the surface of the applicator roller 11 for scraping off excessive silicone oil 9 remaining on said roller 11 so as to be again collected in the tank 8.
The fixing apparatus of FIG. 1 further includes a metallic roller 13 arranged to contact under pressure by suitable urging means (not shown), the surface of the lower fixing roller 7 supplied with the silicone oil 9 by the applicator roller 11 for rotation in the direction of the arrow "c" following the rotation of the lower fixing roller 7, so that the silicone oil 9 applied onto the surface of the lower fixing roller 7 is smoothed or uniformly distributed over said surface to be further supplied to the upper fixing roller 4 for elimination of the problems mentioned earlier. More specifically, in the above arrangement, it is so arranged that the silicone oil unevenly adhering to the surface of the lower fixing roller 7 is uniformly or evenly distributed all over the surface of said roller 7.
However, according to experiments carried out by the present inventors in a manner as described below, it has been fouund that, when the silicone oil is uniformly distributed by the roller 13 in the fixing apparatus as described above, although no particular problem is encountered in fixing copy paper sheets of the same size, soiling due to traces of silicone oil is noticed on the fixed copy paper sheets upon alteration of copy paper size.
More specifically, in the experiments carried out by the use of the fixing apparatus as described above, when copy paper sheets of B4 size were passed after one hundred copy paper sheets of A4 size had been fixed, the soiling due to traces of silicone oil appeared at opposite edge portions of the B4 size copy paper sheets exceeding the A4 size.
Accordingly, it has been found by the present inventors that, in the fixing apparatus of silicone oil application system, particularly in one intended to deal with copy paper sheets of different sizes, the problem related to the soiling due to the traces of silicone oil appearing at such edge portions must be solved besides achieving the uniform distribution of the silicone oil applied onto the fixing rollers.
In connection with the above, the present inventors have concluded that the above problem of soiling due to traces of oil is attributable to the fact that, as shown in FIG. 2, while the silicone oil adhering to the fixing rollers 7 and 4 is consumed by degrees at a central portion C of the path defined between the rollers 7 and 4 as copy paper sheets of small size, for example, A4 size are passed therethrough, the silicone oil at edge portions E other than the central portion C is not consumed and gradually becomes excessive through accumulation, and that even the metallic roller or smoothing roller 13 can not adjust the excessive silicone oil at the edge portions E to a proper amount required for preventing the undesirable offset phenomenon.